Dear all.
Nice one James. You don't waste much time!
So, changing the unpacked model as I described above and with the original 32*13mm section in the tail, running on Methanol at full throttle. The model started straight away and ran for the full 10 cycles (over 2500 iterations), the pressure trace showing a good degree of stability after 4 cycles.
I'm running the model again but with a 29mm *13 section in the tailpipe. Tomorrow I'll run Mikes suggestions to the standard set-up.
I don't want to give you the Thrust figures because I know I have an error in my calculations, my values all are a little on the high side and assume too many things are perfect.
All that's left is to discuss if the unpacked model I'm using is a valid model or not, any suggestions?

James D wrote:Thanks Graham and Larry
I'll go ahead and build it, probably be ready to test on friday.
I really don't mind having to modify it, Should be interesting, now if I could just find some methanol...

James -

Absolutely beautiful!

Yes, make things easy on yourself and try propane for your first shot. If that doesn't cut it, then go to more energetic fuels before you start messing with tuning changes.

I love it when someone has the guts to give a go to one of my designs. Good luck with her !!!

So, changing the unpacked model as I described above and with the original 32*13mm section in the tail, running on Methanol at full throttle. The model started straight away and ran for the full 10 cycles (over 2500 iterations), the pressure trace showing a good degree of stability after 4 cycles.

Wonderful ... by "changing ... as I described above" I presume you mean just the shortening if the intake duct.

I'm running the model again but with a 29mm *13 section in the tailpipe. Tomorrow I'll run Mikes suggestions to the standard set-up.
I don't want to give you the Thrust figures because I know I have an error in my calculations, my values all are a little on the high side and assume too many things are perfect.

Wonderful, again. Let's hope it doesn't throw things too far off the original layout to cast doubt on James' prototype. Of course, his photos show that he hasn't built the intake yet, so he still has some leeway!

All that's left is to discuss if the unpacked model I'm using is a valid model or not, any suggestions?

You and mike, with your 'center of combustion' theory are a full step out of my league, so I can't think of a thing to offer that would be of help. I have made an interesting UFLOW observation about the rear nozzle, though:

If you "flatten" the rear nozzle, (i.e., shorten it without altering the inner or outer diameters while lengthening the middle cone to preserve the overall engine length), you will of course get a sharper pressure reflection back into the chamber. This means the nozzle location becomes more critical. There is yet another effect that makes it critical, too, that I only noticed just a few minutes ago: Flattening the nozzle makes the tail cone act more independently! That is, you can see it "thrashing" at its own resonant open-tube frequency, just like an intake pipe !!! This is superimposed on the general pressure wave, of course. Thus, by repositioning the flattened nozzle, you can "tune" the tail cone into (or out of) resonance with the whole. In fact, the engine acts somewhat (and I emphasize, somewhat) as an asymmetrical two-chambered engine - a forward large chamber with small intake, and a rearward small chamber with a huge intake.

This suggests that you could work through tuning of the overall design by flattening the rear nozzle cone temporarily, adjusting its position until you get everything "sync'd up" the way you like it, then lengthening it out again as desired to take the critical "sharpness" out of the tuning (broaden the resonance of the engine, within reason).

The thing that might be really difficult about this is getting the tail cone gas temps close enough to reality. The resonance of the tail cone, like that of an intake pipe, is going to be highly dependent on temperature. I have recently felt that any cone- or bustle-type tailpipe configuration is going to be radically cooler than a straight pipe equivalent, because of its easier breathing. So, the wave traverse through it will be significantly slower than it is deeper in the engine. This MUST be taken into account (by supplying fairly accurate temp data), since it is such a large part of the total wave path length. I have no idea how to get the accurate local temps needed that would let you know you've got it right.

All my gas temps for UFLOW are just guesses - it's amazing that I ever get anything to come out right at all!

While the forums slept, I developed the full-size drawings shown here for this engine. There is nothing really different about these, except that the level of detail is better than the tiny drawing published earlier, so it might be easier for us ordinary mortals to actually build one. Of course, it needs to be understood that the exact dimensions are still subject to revision, in line with experimental findings.

The last drawing is useless as a full size drawing unless you have a wide printer, like a plotter or something. The first three should each print out on an 8.5 x 11 inch sheet using a 96 DPI printer, giving full scale partial drawings which can be physically pasted together on the "match lines" to form a full-length plan. Grid squares are 1 cm x 1 cm. One thing that might help a little is that on these drawings, color is used to visually distinguish different parts; this may be helpful to some in properly interpreting the drawings.

Working out the main engine body cones using Eric Beck's Cone Calculator (part of his Pulsejet Calculator, freely available from his Website), I have now derived the dimensions of the cone sheets for the main body of this engine. Each sheet can be described in only three dimensions, from which a template can be made: the Outer Radius, the Inner Radius, and the subtended Angle. Here are the calculated data for the five cones that make up the engine shell:

I have rounded each figure to the nearest mm so as not to imply a ludicrous level of required precision. Errors of a mm or less on any of these dimensions should be meaningless on an engine of this size.

I tried to run her on propane yesterday, after ten minutes of playing with fuel and air pressure she barked into life.'-)
The frequency peaked at 320 Hz and as I increased the fuel it dropped slightly.
I will try and get a good thrust measurement today and a longer test run to see if the hot spot moves down the tail pipe.

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Dear James.
What a Joy. Many thanks for that.
Please can you detail any mods you had to make.

While we were away. 'Dear Larry.

Both Unpacked models run well on my Methanol settings. The 32mm*13mm model (your original) produces slightly more thrust than the 29mm*13mm option. Note, for these tests I'm using the unpacked model that I proposed it has an induction path length equal to the centreline path length down the folded model and the CC front cone has been extended to make up the difference.

Regards

Graham.'

And

2 things that you could pass on to James if he has any difficulties:

Reducing the start of the induction pipe down to about 20mm should help the starting.

The induction pipe might benefit from being a bit longer. A 5 to 10mm extension perhaps built as part of the reducer.

Dear Mike.
Very many thanks for all the work you and Ben must have done to get this site up and running.

Dear Larry and James.
On the video you can see the early combustion is taking place at the 23% point of the packed model. This is one of the required combustion locations as predicted by Mikes analysis and also the NUDiS models I'm running. This location corresponds well to the 37% (approx) location for the unpacked model. Of interest the nodal point on Larrys unpacked model is located at the other possible location, 23%. If we could move that CofC of James motor right up close to the sparkplug that would correspond to the 23% location. The analysis suggests that peak combustion pressure would be higher and thrust a little better. We might be able to achieve this by lengthening the induction pipe a little - perhaps an internal sliding pipe.

Dear Larry.
This is the Unfolded model I used in my NUDiS based program. The 32*13 and the 29*13 tail sections were tested with success using this layout. I apologise for using your drawing it was the quickest way.
This model ran (on Methanol) at 394Hz.

Graham
I made no deliberate mods, however the overall length is possibly 1mm short and the intake is 0.5mm smaller diameter than Larrys drawing, other than that is pretty accurate and internal transitions are smooth.

James D wrote:I tried to run her on propane yesterday, after ten minutes of playing with fuel and air pressure she barked into life.'-)
The frequency peaked at 320 Hz and as I increased the fuel it dropped slightly.
I will try and get a good thrust measurement today and a longer test run to see if the hot spot moves down the tail pipe.

James, wonderful!!! Way to go, Larry, Graham.

Graham, inspired work, putting on that intake transition on the unfolded model. I was going down a similar path. General conclusion for me is you just can't unfold it and have the same motor, but you can prove out those diameters you depend on for confinement.

Congradulations Larry and James for a job well done. It looks good, sounds excellent, and is obviously pushing along on that test stand quite well. I'm very happy for you larry as your design ability is second to none. Excellent work!

Just saw the video, after an agonizing download thru our modem (things are a whole lot nicer at my day job). I HAD to watch it five or six times. UNBELIEVABLE ... UNBELIEVABLE! That 320 hz is, I think, actually a little faster than my UFLOW model showed, though I haven't looked at it again.

What a wonderful build, James! Thank you, thank you! I love it when someone else builds a prototype for me and gets it working! You did a great job of building and testing this lady! NOTE TO OTHERS: There was no private communication between myself and James during this build, and he did not have the full-size plans I just published ... only my original crude scale drawing to work from.

Congratulations, James! And, many thanks to you all for your congratulations. REMEMBER: This was tightly based on Graham's and Nick's work developing the original cylinder-and-cone Type 07 tailpipe (see http://www.pulse-jets.com/phpbb2/viewtopic.php?t=1813 ) - THEY did all the heavy lifting! I just "prettied it up" a bit. As far as I know, that was the FIRST FWE with a fully non-cylindrical tailpipe ever actually built and run!

Thank you too, Graham, for all your recent NUDIS work verifying this pipe! I'm sure there were times when you could have been more profitably doing something else. I really appreciate your fine efforts.

I can hardly wait to see what the thrust figure will come out to! James, what did you end up with for a total engine weight (in ounces, if possible)? Do you have a way of getting the TSFC? (I guess you do, since you're interested in doing a "long run" anyway, and you must have something around that can weigh the propane before and after.) Does starting seem completely conventional (certainly looks like it in the video clip!)? Is there anything you found unusual or unexpected in the building, startup or running of this motor?

James, thanks again for your ability and your willingness to take this on as a prototype for independent testing! True grit, man! Wonderful work!

I ran it again today.
Start up was quite simple and easy to repeat, but it did seem to require more air than a standard FWE. I will make a note of the minimum air and fuel pressures next test.
The fuel pipe is approximately 2mm ID and terminates about 25mm from the combustion chamber, this is only the second position I tried and probably isnâ€™t optimal, but it worked so I left it there.
I donâ€™t know when Iâ€™ll be able to run it long enough to get a meaningful TSFC figure, probably not for a while.

I measured thrust as 2.6lbs, It lifted just under 1200ml of water. At the start of the video above, when it first moves on the stand itâ€™s already lifting 750ml of water.
Fuel pressure could be increased quite a lot beyond the point of maximum thrust before it flamed out.

Iâ€™ve attached a picture showing the heat pattern after two minutes of running, the heat has spread along the bottom of the tailpipe, the top must be cooled by the intake airflow.

Larry.
What have you been doing? 2.6Lbs straight off the drawing board!!!. And the motors so nice and short. We must try this beast on Methanol, could get up to 30% extra if you can get the injection correct.
Below is a model I'm trying at the moment but before anybody tries it I'd like opinions because it would require changing the location where the induction pipe enters the CC - that's if I'm packing it correctly. The induction pipe would start at the same point along the folded motor but would have to be mounted some small distance nearer the sparkplug. The early projections for this model are for a significant increase in thrust but I must do a full run first and check stability.